Heretofore, some structures have employed a vibration isolating construction specially designed to minimize the effect of seismic vibrations in view of the properties of the seismic vibrations. One such vibration-isolated structure incorporates a vibration isolator disposed between the ground and the structure for preventing vibrations of the ground due to earthquakes from being transmitted to the structure (building) as much as possible.
According to such a vibration isolator, as shown in FIGS. 15A and 15B of the accompanying drawings (FIG. 15A is an elevational view and FIG. 15B is a plan view), a building 301 is not fixed to a foundation 302, but a plurality of guiding apparatuses 303 for allowing the building 301 to move on the foundation 302 are disposed between the foundation 302 and the building 301. When seismic forces higher than a certain level are applied, the building 301 slides on the guiding apparatuses 303 to prevent the seismic forces from acting on the building 301.
The applicant of the present invention has previously proposed three-dimensional guiding apparatuses for use as the above guiding apparatus in Japanese patent application No. 9-37072. The proposed three-dimensional guiding apparatuses are roughly grouped into two types. FIG. 12 of the accompanying drawings shows in perspective one of the types of the proposed three-dimensional guiding apparatus. As shown in FIG. 12, the three-dimensional guiding apparatus has a base 140, a first curved guiding apparatus 150 mounted on the base 140 and having an arcuate track, a second curved guiding apparatus 160 disposed above the first curved guiding apparatus 150 and having a plane of movement along an arcuate track which crosses the plane of movement of the first curved guiding apparatus 150, and an intermediate member 170 positioned between the first curved guiding apparatus 150 and the second curved guiding apparatus 160 and interconnecting the first curved guiding apparatus 150 and the second curved guiding apparatus 160.
The first and second curved guiding apparatuses 150, 160 comprise track rails 151, 161 vertically curved at a predetermined curvature and having ball rolling grooves 153, 163 defined along an arcuate shape of predetermined curvature in mutually confronting surfaces, bearing blocks 152, 162 having an U-shaped cross section astride the track rails 151, 161 and having ball rolling grooves defined in alignment with the ball rolling grooves in the track rails 151, 161 along an arcuate shape of predetermined curvature, and a plurality of balls (not shown) disposed for bearing loads between the ball rolling grooves in the track rails 151, 161 and the ball rolling grooves in the bearing blocks 152, 162. The intermediate member 170 which interconnects the first curved guiding apparatus 150 and the second curved guiding apparatus 160 is in the form of a rigid block.
FIG. 13 of the accompanying drawings is a view showing the manner in which the three-dimensional guiding apparatus shown in FIG. 12 is used.
As shown in FIG. 13, three-dimensional guiding apparatuses 303 have respective spherical guide tracks whose centers of curvature are established separately, rather than as a common center, on a building 301. Between the building 301 and the three-dimensional guiding apparatuses 303, there are provided tilt absorbing mechanisms 304 for allowing tilts generated between the building 301 and the three-dimensional guiding apparatuses 303 when vibrations occur. Each of the tilt absorbing mechanisms 304 may comprises a universal joint, a spherical bearing, or an elastic member of rubber or the like.
FIG. 14 of the accompanying drawings is a front elevational view showing the other type of the three-dimensional guiding apparatus.
As shown in FIG. 14, the three-dimensional guiding apparatus comprises a base 140, a first curved guiding apparatus 150 mounted on the base 140 and having an arcuate track, a second curved guiding apparatus 160 disposed above the first curved guiding apparatus 150 and having a plane of movement along an arcuate track crossing the plane of movement of the first curved guiding apparatus 150, and an intermediate member 170 positioned between the first curved guiding apparatus 150 and the second curved guiding apparatus 160 and interconnecting the first curved guiding apparatus 150 and the second curved guiding apparatus 160. Amoving base 180 on which a building is supported is fixedly mounted on the second curved guiding apparatus 160. In this example, the intermediate member 170 comprises a universal joint for absorbing tilts between the first curved guiding apparatus 150 and the second curved guiding apparatus 160. The intermediate member may comprise a spherical bearing, an elastic member such as a spring or a rubber member, rather than the universal joint.
The first and second curved guiding apparatuses 150, 160 comprise track rails 151, 161 vertically curved at a predetermined curvature and having ball rolling grooves 153, 163 defined along an arcuate shape of predetermined curvature in mutually confronting surfaces, bearing blocks 152, 162 having an U-shaped cross section astride the track rails 151, 161 and having ball rolling grooves defined in alignment with the ball rolling grooves in the track rails 151, 161 along an arcuate shape of predetermined curvature, and a plurality of balls (not shown) disposed for bearing loads between the ball rolling grooves in the track rails 151, 161 and the ball rolling grooves in the bearing blocks 152, 162.
In the absence of seismic vibrations, the vibration isolating construction with the above three-dimensional guiding apparatus allows the building to be stably positioned in a steady position on the three-dimensional guiding apparatus. Even when an earthquake occurs and causes the ground to vibrate, the ground and the building are isolated against the transmission of vibrations by the three-dimensional guiding apparatus, so that large vibrations will not be transmitted to the building. After seismic vibrations are settled, any vibrations of the building with respect to the ground are attenuated, and the building is stabilized in the steady position on the three-dimensional guiding apparatus.
In order for the three-dimensional guiding apparatus proposed in Japanese patent application No. 9-37072 to keep the building in a horizontal state when the building suffers vibrations caused by earthquakes or the like, it is necessary to provide a tilt absorbing mechanism between the first curved guiding apparatus and the second curved guiding apparatus. The tilt absorbing mechanism comprises a universal joint, a spherical bearing, or an elastic member such as a spring or a rubber member.
If the tilt absorbing mechanism comprises a universal joint or a spherical bearing, then since the overall weight of the building has to be borne by a sliding portion such as a crisscross shank (universal joint) or a spherical seat having a small area, stresses developed in the sliding portion become unduly larger than those developed in other members, and tend to be broken or worn in a short period of time.
If the tilt absorbing mechanism comprises an elastic member such as a rubber member, then it is capable of bearing only loads within an elastically deformable range, and incapable of bearing higher loads. Another problem is that the elastic member is poor in durability as it is liable to suffer flatting due to aging. That is, the three-dimensional guiding apparatus proposed in Japanese patent application No. 9-37072 is unable to bear heavy loads because of the tilt absorbing mechanism.
It is an object of the present invention to provide a three-dimensional guiding apparatus which has a tilt absorbing function, is cable of bearing heavy loads, and has excellent durability.